Fluid ducts



vMay 13, 1969 D. PIERCE 3,443,598

FLUID DUCTS Filed Dec. s. 1965 sheet of 2 FIG. 2.

FIG. 3.

nventor m n? AWM@ D. PIERCE FLUID DUCTS May V13, 1969 Z of 2 Sheet Filed Dec. 5. 1965 FIG.

INVENTOR DONALD PIERCE l Ri TORNEYS United States Patent O 3,443,598 FLUID DUCTS Donald Pierce, Aldershot, England, assignor to Minister of Technology in Her Britannie Majestys government of the United Kingdom of Great Britain and Northern Ireland, London, England Filed Dec. 3, 1965, Ser. No. 511,534 Claims priority, application Great Britain, Dec. 4, 1964,

49,443/ 64 Int. Cl. FlSd 1/02; F161 11/00; F02b 27/00 U.S. Cl. 138--45 4 Claims ABSTRACT F THE DISCLOSURE A variable area duct for fluid, having a flexible wall pivotally connected to a fixed base by means of a plurality of swing links so that when a load is applied generally in the plane of the wall, its profile is varied.

This invention relates to fluid ducts. The invention is particularly concerned with intake and exhaust ducts for aircraft, and, fluid flow test apparatus generally known as wind tunnels.

When the speed of the fluid flow through a duct is near or above supersonic it is sometimes desirable that the profile of the duct be changed in order to obtain the most advantageous conditions of flow.

In the case of a wind tunnel an article such as a model of an aircraft wing section is supported in the working section of the tunnel and the characteristics of the flow and the response of the model are measured and recorded in one or more of several well known methods. The working section is normally just downstream of a convergentdivergent throat section. In certain cases it is desirable that the speed of the fluid flow over the model should be changed quickly as a test proceeds and even in response to readings received from the model itself under test.

It is alreadytknown to change the profile of the throat of the tunnel whereby for a given power input to the fluid flow through the tunnel the air speed at a given section downstream of the throat is varied. The profile may be changed by having interchangeable throat portions of different profile and it is also known to have a flexible wall portion, the profile of which is changed by means of hydraulic jacks which act substantially normal to the general direction of flow to deform the tunnel wall.

According to the present invention a fluid duct has a flexible wall portion which is supported in a predetermined profile Iby arms which are connected at their one ends to the flexible wall at moving connecting points and at their other ends to a fixed base at fixed connecting points and power means are provided for applying tension to the flexible wall to cause it to move whereby the one ends of the arms move with respect to their other fixed ends and to change the profile of the wall.

The arms may comprise cantilever type springs rigidly fixed to the fixed base at the fixed connecting points but pivotally secured at their other ends to the `flexible wall.

Preferably the arms comprise swinging links which are pivotally secured to the flexible wall and the fixed base at their opposite ends, respectively.

' Preferably a fluid duct according to this invention is of convergent-divergent form and of rectangular cross section at the throat and comprises two opposing fixed parallel walls and two opposing flexible walls of variable profile.

One preferred arrangement of a fluid duct according to this invention, comprises a flexible Wall supported pivotally at the moving ends of a set of swinging links which are pivotally supported at their other fixed ends to define a predetermined profile, and a control jack and a secondary jack which are connected to the swinging links at opposite ends of the flexible wall portion, respectively, the control jack being operative to apply a controlling torque in the one sense to the one end link about its fixed pivot and the secondary jack being operative to apply damping torque in the other sense to the other end link about its fixed pivot whereby the flexible wall portion is maintained in a condition'of tension and the angular position of the one end link may be varied to cause the links to swing about their fixed pivots and the profile of the wall to change.

The invention is illustrated by the diagrammatic drawings accompanying the specification of which:

FIGURE l illustrates the working section or throat of a wind tunnel according to the invention,

FIGURE 2 is a sectional side elevation of the flexible wall portion of a wind tunnel on the line II-II of FIG- URE 3,

FIGURE 3 is 'a sectional end elevation on the line III--III of FIGURE 2, and

FIGURE 4 illustrates the principle used for obtaining certain desired profiles, and

FIG. 5 is a side elevation of part of the flexible wall portion of a wind tunnel showing an alternative arrangement according to the invention.

Referring first to FIGURE 1 the throat or working section of a wind tunnel is defined by ltwo opposed parallel flat walls 11, 11 and two opposed flexible walls 12, 12 respectively. The direction of air flow is shown by the arrow A. In a particular case under consideration the flow speed will be subsonic at a section 13, sonic at the narrowest section 14 of the throat, and, supersonic at a section 15 where a model to be tested will be placed.

Referring now to FIGURES 2 and 3, the flexible wall portion of a wind tunnel is defined by a flexible plate .16.

A set of arms 17 17, each comprising a frame member as shown in FIGURE 3, are pivotally supported by fixed pivot rods 18 18 to a fixed base 19 at their one ends and at their other ends are pivotally connected by moving pivot rods 20 20 to lugs 21 21 at the outer face of the plate 16. At the upstream and downstream end regions the flexible plate 16 is pivotally sesecured by rods 22, 23 to swinging end frames 24, 25, respectively, which are pivotally supported by rods 26, 27 on the fixed base 19. A control jack 28 is connected to the frame 25 at 29 and a secondary tensioning jack 30 is connected to the frame 24 at 31. At the upstream end the flexible plate 16 is slotted and fits between a cover piece 32 and a pivotted end block 33 which are secured to each other by studs 34, 34 and spaced apart by washers at 35, 35. A fixed part of the tunnel wall is shown at 36 and carries a flexible cantilever section 37 which overlaps the cover piece 32.

In operation the control jack 28 is set in a predetermined position and the secondary tensioning jack 30 aplies a tensioning load to the flexible plate 16 through the end frame 24. For a given setting of the control jack 30 the swinging arms 17 will cause the flexible wall 16 to define a given profile for example as shown in FIGURE 2 and as defined by the points 20 20. To change the profile of the flexible wall the control jack 28 is set in a second position whereby the tension exerted by the secondary jack in combination with that exerted by the control jack will cause the end frames 24, 2S and the arms 17 117 to swing about their fixed pivots and the profile of the flexible plate to change for example as indicated by the dotted line 16a and the points 20a 20a.

It is to be noted that the invention is equally applicable to a hydrodynamic testing tunnel.

Referring now ot FIGURE 4, three wall profiles which will result in uniform fluid flow are indicated at X, X1 and X2, respectively. It will be seen that if a point A on profile X is required to move to points A1 and A2 on the other profiles X1 and X2, respectively, there is only one length of arm and one location for the fixed pivot point Ap which can be chosen. Similarly a second point B will move to points B1 and B2 about a second fixed pivot point Bp.

Referring to FIG. 5, a portion of the flexible wall of a wind tunnel is shown at 51 and a fixed base member at 52. The flexible wall 51 is supported by a set of cantilever type spring arms, four of which are shown at 53. The arms 53 are rigidly secured to the base 52 by brackets 54 and at their other ends carry pivot pins 55, which, in turn, engage corresponding bearing brackets 56 secured to the fiexible wall. Tension is applied to the flexible wall in a similar manner as described above with reference to FIGS. 1 to 3 with the result that arms 54 deflect cantilever fashion, and permit a change in the profile of the flexible wall.

The invention is equally applicable to the intake or exhaust duct of an aircraft jet engine particularly for fiight speeds in the region of the speed of sound and above. In such cases the profile could be changed in accordance with changes in flight speed and/ or other flight characteristics by the pilot or automatically.

I claim:

1. A variable area duct for fluid comprising a flexible wall, a plurality of swing links, a fixed base, means pivotally connecting one end of each of said links to said wall, means pivotally connecting the other end of each of said links to said base, and power means operably connected to said wall and adapted to apply loads generally in the plane of said wall so that said one end of each of said links moves with respect to said other end thereof to vary the profile of said wall.

2. A variable area duct Afor fluid as claimed in claim 1, further comprising two opposing fixed parallel walls, and

.4 wherein two opposing flexible walls are provided, said walls defining a duct of convergent-divergent conguration and of rectangular cross section.

3. A variable area duct for fluid comprising a flexible wall, a fixed base, a plurality of cantilever spring arms each secured at one end to said base, means pivotally connecting the other end of each of said spring arms to said wall, and power means operably connected to said Wall and adapted to apply loads generally in the plane of said wall so that said other end of each of said arms lmoves with respect to said one end thereof to vary the profile of said wall.

4. A variable area duct for fiuid as claimed in claim 3, further comprising two opposing fixed parallel walls, and wherein two opposing flexible walls are provided, said walls defining a duct of convergent-divergent configuration and of rectangular cross section.

References Cited UNITED STATES PATENTS 2,472,949 6/ 1949 Jackson 138-45 2,486,287 10/ 1949 Jackson 138-45 2,546,673 3/1951 Mattix et al. 13S-45 2,570,129 10/1951 Johnson 138-45 X 2,580,228 12/ 1951 Johnson 138-45 X 2,593,420 4/ 1952 Diehl 138-45 X 2,791,240 5/ 1957 Storms et al. 138-45 2,934,966 5/1960 Wood 138-45 X 3,045,705 7/ 1964 Hausammann 138-45 3,069,842 12/ 1962 Price 138--46 3,295,555 1/1967 James et al 138-45 HOUSTON S. BELL, JR., Primary Examiner.

U.S. C1. X.R. 137-15.1 

